Picture size

[TJ]

Something that's been bugging me recently...I've only been able to post small-sized pics over the last few weeks. The ones I used to post were much larger, at least visually. What do I have to change in order to post larger ones? The resolution? With my ACDSee software, I seem to only be able to change the width and height.

For example, there is a randomly chosen pic I posted long ago, and which was accepted by the server:

Here are the stats for this picture:

MegaPixels: 0.34
Width: 699
Height: 492

But now, about the largest pic I am able to post without it being rejected by the server is this size:

MegaPixels: 0.17
Width: 545
Height: 311

John's recent photo seems quite large...

...but is actually only:

MegaPixels: 0.17
Width: 545
Height: 311

The same as by brevipes pic, but showing much larger on the screen.

What gives?

 

[john]

Hi Tim,

Sorry you've been having problems. I know what's wrong though.

Before I get into the explanation, I just want to say that whatever method you're using to get these "Megapixels" values is bogus. To get the megapixel value of a photo simply multiply the width by the height in pixels. Some of your width and height values are also erroneous...

That aside, I have two words (which are actually five): JPEG compression. I use it and I think you should too. You appear to have used it for the first image.

The true statistics of the 3 photos you've shown here are:

Top one (Hynobius egg sac?)
=============================
Width: 699 pixels
Height: 492 pixels
File size: ~100 kilobytes
You appear to have used compression here.

Middle one (Pachytriton brevipes)
=================================
Width: 545 pixels
Height: 311 pixels
File size: ~175 kilobytes
Either you have compression turned off for saving this file or it's set very low (maybe 95%?).

Bottom one (Cynops encsicauda popei)
====================================
Width: 700
Height: 475
File size: ~77 kilobytes
Compression: 85%

That photo of my popei metamorph was saved using 85% JPEG compression to yield the above file size.

There are limits set on the server - it will only accept images with maximum dimensions 1025x1025 pixels (quite large for a web site) and that have a file size of 150 kilobytes or smaller.

So the moral of the story is to look in your ACDSee software and find the option for JPEG compression (probably a button on the dialog box that comes up after you click "save as" JPEG).

So any opinions on my funny looking popei in the other topic?

 

[TJ]

I think I may have found what you told me to look for:

Wow, it works! Thanks a lot, John

I spent half the day looking trying to figure this out. If I'd just read your post more carefully, I wouldn't have wasted so much time.

The problem was that I was using 100% compression. The photo above is 70%. I have Photoshop installed in my computer but it is simply too confusing for me. I think I'll stick with ACD FotoCanvas for a while.

One thing the software help section advises me to do, which I haven't really followed to date, is to maintain image quality by reducing images only by 33%, 50%, or 66%. It says other percentages can distort the aspect ratio.

The above image hasn't been worked on much and I just posted it to see what kind of screen size I can get.

I shall take a look at your funny looking popei and get back to you on that

 

[TJ]

The option for JPEG compression, by the way, was indeed a button on the dialog box that comes up after I click "save as" JPEG.

I readjusted the size of a few recent pics that I've posted, namely those at:

http://www.caudata.org/forum/messages/13/15941.html?1086111244

For those, I tried out 82% compression. Would you recommend 85%?

As for what I said about reducing images by 33%, 50%, or 66%, well, that's really out of the questions given the size of the original pics I take!

I read that if a JPEG file is saved as JPEG file once, then altered and saved again as a JPEG file, it decreases in quality, and that it should be saved as something else if future alterations are anticipated. Is this so?

 

[TJ]

Also, I notice that at some reduction ranges, I get a criss-cross pattern as seen over the white mushroom stem in this pic:

http://www.caudata.org/forum/messages/13/16441.jpg

 

[john]

The grid/criss-cross pattern: I think it might be a quirk in the way your program does JPEG compression and it'll become more noticeable with higher compression.

I would recommend 80%-85% compression for most images. I usually use 85%.

JPEG is a lossy form of compression - it looses data every time you save it with compression. So don't keep modifying the same file and re-saving it.